i think the value of z is 10.
how:-
step 1:- --y is evaluated which become -11.
step 2:- (-11) will multiple with b which become -22
step 3:- this (-22) get devided by a now intermidiate result will be -5
step 4:- now expression become as z=x++ - -5;
step 5 :- -5 become +5
step 6:- here the main game start the priority of post-increment is lower then assignement operater that's why first the value of x which is 5 is added with intermidiat result +5 which become 10 and this 10 get assigne into variable z .
step 7:- variable x increment its value by 1 and become 6.

Don't forget that x++ means POSTincrement and ++x means PREincrement. That means before and after, and is usually before or after some execution point. So the equation in some senses (but definitely not all) is equivalent to:

Don't forget that x++ means POSTincrement and ++x means PREincrement. That means before and after, and is usually before or after some execution point. So the equation in some senses (but definitely not all) is equivalent to: